In a typical bar screen apparatus for wood chips, with a length on the order of 10 feet, there often arises a problem of maintaining adequate bar rigidity, i.e. stiffness, over the entire length of the bars. Without sufficient stiffness, the bars deflect to an extent, particularly near mid-length, such that the size of the screen openings will vary over the length of the screen, degrading performance and predictability of results. To correct this, the bars comprising the screen typically have a fairly large thickness, so that the percentage of the screen area that is open to passage of acceptable-size material is only approximately 35%. Alternatively, the individual bars can be supported in some fashion at various points along the lengths thereof. These intermediate support elements can interfere, however, with the passage of acceptable-size material.
In addition to the above-described undesirable deflection effect which occurs over the length of the bars, there is often difficulty in obtaining adequately straight bars from a manufacturer, i.e. the bars are often slightly bowed or crooked. Bars having the required straightness are initially expensive, and also are expensive to replace. In general, such bar screens are expensive to maintain.